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    1: *> \brief \b ZLACRT performs a linear transformation of a pair of complex vectors.
    2: *
    3: *  =========== DOCUMENTATION ===========
    4: *
    5: * Online html documentation available at
    6: *            http://www.netlib.org/lapack/explore-html/
    7: *
    8: *> \htmlonly
    9: *> Download ZLACRT + dependencies
   10: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/zlacrt.f">
   11: *> [TGZ]</a>
   12: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/zlacrt.f">
   13: *> [ZIP]</a>
   14: *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/zlacrt.f">
   15: *> [TXT]</a>
   16: *> \endhtmlonly
   17: *
   18: *  Definition:
   19: *  ===========
   20: *
   21: *       SUBROUTINE ZLACRT( N, CX, INCX, CY, INCY, C, S )
   22: *
   23: *       .. Scalar Arguments ..
   24: *       INTEGER            INCX, INCY, N
   25: *       COMPLEX*16         C, S
   26: *       ..
   27: *       .. Array Arguments ..
   28: *       COMPLEX*16         CX( * ), CY( * )
   29: *       ..
   30: *
   31: *
   32: *> \par Purpose:
   33: *  =============
   34: *>
   35: *> \verbatim
   36: *>
   37: *> ZLACRT performs the operation
   38: *>
   39: *>    (  c  s )( x )  ==> ( x )
   40: *>    ( -s  c )( y )      ( y )
   41: *>
   42: *> where c and s are complex and the vectors x and y are complex.
   43: *> \endverbatim
   44: *
   45: *  Arguments:
   46: *  ==========
   47: *
   48: *> \param[in] N
   49: *> \verbatim
   50: *>          N is INTEGER
   51: *>          The number of elements in the vectors CX and CY.
   52: *> \endverbatim
   53: *>
   54: *> \param[in,out] CX
   55: *> \verbatim
   56: *>          CX is COMPLEX*16 array, dimension (N)
   57: *>          On input, the vector x.
   58: *>          On output, CX is overwritten with c*x + s*y.
   59: *> \endverbatim
   60: *>
   61: *> \param[in] INCX
   62: *> \verbatim
   63: *>          INCX is INTEGER
   64: *>          The increment between successive values of CX.  INCX <> 0.
   65: *> \endverbatim
   66: *>
   67: *> \param[in,out] CY
   68: *> \verbatim
   69: *>          CY is COMPLEX*16 array, dimension (N)
   70: *>          On input, the vector y.
   71: *>          On output, CY is overwritten with -s*x + c*y.
   72: *> \endverbatim
   73: *>
   74: *> \param[in] INCY
   75: *> \verbatim
   76: *>          INCY is INTEGER
   77: *>          The increment between successive values of CY.  INCY <> 0.
   78: *> \endverbatim
   79: *>
   80: *> \param[in] C
   81: *> \verbatim
   82: *>          C is COMPLEX*16
   83: *> \endverbatim
   84: *>
   85: *> \param[in] S
   86: *> \verbatim
   87: *>          S is COMPLEX*16
   88: *>          C and S define the matrix
   89: *>             [  C   S  ].
   90: *>             [ -S   C  ]
   91: *> \endverbatim
   92: *
   93: *  Authors:
   94: *  ========
   95: *
   96: *> \author Univ. of Tennessee
   97: *> \author Univ. of California Berkeley
   98: *> \author Univ. of Colorado Denver
   99: *> \author NAG Ltd.
  100: *
  101: *> \ingroup complex16OTHERauxiliary
  102: *
  103: *  =====================================================================
  104:       SUBROUTINE ZLACRT( N, CX, INCX, CY, INCY, C, S )
  105: *
  106: *  -- LAPACK auxiliary routine --
  107: *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
  108: *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
  109: *
  110: *     .. Scalar Arguments ..
  111:       INTEGER            INCX, INCY, N
  112:       COMPLEX*16         C, S
  113: *     ..
  114: *     .. Array Arguments ..
  115:       COMPLEX*16         CX( * ), CY( * )
  116: *     ..
  117: *
  118: * =====================================================================
  119: *
  120: *     .. Local Scalars ..
  121:       INTEGER            I, IX, IY
  122:       COMPLEX*16         CTEMP
  123: *     ..
  124: *     .. Executable Statements ..
  125: *
  126:       IF( N.LE.0 )
  127:      $   RETURN
  128:       IF( INCX.EQ.1 .AND. INCY.EQ.1 )
  129:      $   GO TO 20
  130: *
  131: *     Code for unequal increments or equal increments not equal to 1
  132: *
  133:       IX = 1
  134:       IY = 1
  135:       IF( INCX.LT.0 )
  136:      $   IX = ( -N+1 )*INCX + 1
  137:       IF( INCY.LT.0 )
  138:      $   IY = ( -N+1 )*INCY + 1
  139:       DO 10 I = 1, N
  140:          CTEMP = C*CX( IX ) + S*CY( IY )
  141:          CY( IY ) = C*CY( IY ) - S*CX( IX )
  142:          CX( IX ) = CTEMP
  143:          IX = IX + INCX
  144:          IY = IY + INCY
  145:    10 CONTINUE
  146:       RETURN
  147: *
  148: *     Code for both increments equal to 1
  149: *
  150:    20 CONTINUE
  151:       DO 30 I = 1, N
  152:          CTEMP = C*CX( I ) + S*CY( I )
  153:          CY( I ) = C*CY( I ) - S*CX( I )
  154:          CX( I ) = CTEMP
  155:    30 CONTINUE
  156:       RETURN
  157:       END